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Is it necessary to install a downhole safety valve in a subsea oil/gas well?
6.2.3 HAZOP of the BOP handling procedure
In an overall risk assessment the identification of hazards and hazardous events are important.
The implementation of a procedure HAZOP on a workover will help identifying the hazards
and its potential consequences. A complete HAZOP of a workover is to comprehensive for this
thesis and the competence of the author. In this study only the handling of the Blowout
preventer (BOP) is considered.
The HAZOP of the BOP handling procedure provided in this thesis has not been subject to a
group discussion and a HAZOP team. The outcome will be fully dependent on the authors
understanding of the problem. Important issues might have been left out and the weighing of
criticality may not have been done to the satisfaction of all readers.
In the traditional HAZOP analysis the guide-words; NO, MORE, LESS, AS WELL AS, etc.
are used. In a procedure HAZOP these words are, from some point of views, not as well suited.
Instead a set of guide-words in interest for the specific analysis are developed for the specific
procedure. The author experimented with the use of such guide-words in the procedure
HAZOP without success. The traditional guide-words are of a general character and easier to
apply to the different procedures in the study of BOP handling. An understanding of why this
guide-word is applied is given for each of the steps in the “causes”-column of the HAZOPsheet.
The need for more specific guide-words was therefore neglected. Traditional guidewords
are also more common and easier to understand. As a result the traditional guide-words
are applied in this thesis. The guide-words used and their meaning is presented in appendix E.
6.2.4 The BOP handling procedure
In this chapter a Blowout preventer (BOP) handling procedure is described. This procedure
will be analysed systematically as a part of a procedure HAZOP. The procedure is only used to
illustrate the employment of a HAZOP study and is therefore reduced. If a full HAZOP study
of the BOP handling procedure is wanted a more extensive description of each step should be
done.
1. The BOP is tested on a hub
2. The AX-seal ring on the BOP is checked
3. The BOP is moved by forklift truck over the hole on the cellar deck.
4. A riser pipe is lifted off the pipe rack with the pipe handling equipment
5. The riser pipe is lowered through the drilling deck and screwed on to the top of the
BOP by an iron roughneck.
6. The BOP is lifted off the fork truck by a riser elevator, lowered and hung at the drilling
deck.
7. The roughneck screws a new riser pipe on and the riser elevator is used to lower the
riser with the BOP attached.
8. This procedure is repeated until the BOP is lowered to the seabed.
9. The guideline wires are tightened to find the right position for the BOP
10. The BOP is connected to the wellhead
11. The BOP is pressure tested for leakage in the AX-seal
12. Workover is performed through BOP
13. BOP is disconnected from wellhead
14. The BOP is raised with the riser elevator
15. Guidelines are loosened to move BOP away from well
Diploma thesis, NTNU 2002
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